Methods and Breeding Tools of Seed Production in Variety and Hybrid PDF

**Methods and breeding tools of seed production in variety and hybrid** Varieties: BREEDING PRINIPLES ============================= Classification of vegetables according to Pollination ===================================================== It is important to know which vegetable crops are self-po...

**Methods and breeding tools of seed production in variety and hybrid** Varieties: BREEDING PRINIPLES ============================= Classification of vegetables according to Pollination ===================================================== It is important to know which vegetable crops are self-pollinated and which are cross-pollinated for growing vegetables for seed production. The following are the classification of vegetables based on the pollination. +-----------------------------------------------------------------------+ | ### Highly Cross-pollinated | +=======================================================================+ | i. | +-----------------------------------------------------------------------+ | ii. | +-----------------------------------------------------------------------+ | Often Cross-pollinated | +-----------------------------------------------------------------------+ | Limabean, egg plant, okra, chilli, sweet pepper. | +-----------------------------------------------------------------------+ | ### Highly Self-pollinated | +-----------------------------------------------------------------------+ | Tomato, cluster bean, french bean, cowpea, dolichos bean, garden pea, | | | | lettuce, methi. | +-----------------------------------------------------------------------+ Self-pollination occurs by reason of floral structure and any cross-pollination takes place is affected by insect-pollinators is often cross-pollinated crops. The frequency of such-cross-pollination is higher in second group. It should be noted that cabbage, cauliflower, knol-khol, sprouting broccoli and brussel's sprout are cultivars of *Brassica oleracea* which can freely cross with each other. Similarly both garden beet and palak, beet leaf, sugar beet, swiss chard are cultivars of *Beta vulgaris* also crossing with each other. Hot pepper (chilli) and sweet pepper (Capsicum) are cultivars of *Capsicum annuum*. The following are the breeding systems, sex form and growth habit of the cross-pollinated vegetable crops. +-----------------+-----------------+-----------------+-----------------+ | ##### Breeding | **Sex form** | **Growth | **Vegetable | | system | | habit** | crops** | +=================+=================+=================+=================+ | Highly cross -- | Hermaphrodite | Annual | Amaranth\*, | | pollinating | | | spinachbeet | | | | [Biennial]{.und | (Palak)\*, | | | | erline} | chenapodium. | | | | | | | | | i. Self-incomp | Cabbage, | | | | atible | cauliflower, | | | | | (Late | | | | ii. Self-fertil | varieties), | | | | e | knol-khol, | | | | | brussels | | | | | sprout, | | | | | sprouting | | | | | broccoli, kale, | | | | | radish, turnip, | | | | | garden beet | | | | | | | | | | Carrot, onion, | | | | | cauliflower | | | | | (some | | | | | varieties) | +-----------------+-----------------+-----------------+-----------------+ | | Monoecious | Annual | Bottle gourd, | | | | | bitter gourd, | | | Dioecious | Annual | sponge gourd, | | | | | ridge gourd, | | | | Perennial | snake gourd, | | | | | ash gourd, | | | | | cucumber, | | | | | pumpkin, | | | | | squash, pointed | | | | | gourd, Indian | | | | | squash, long | | | | | melon, | | | | | watermelon, | | | | | muskmelon\*\*, | | | | | sweet corn\* | | | | | | | | | | Spinach\* | | | | | | | | | | Asparagus, | | | | | pointed gourd | +-----------------+-----------------+-----------------+-----------------+ | Often | Hermaphrodite | Annual | Bhendi (Okra), | | cross-pollinati | | | Lima bean, | | ng | | | Chillies | +-----------------+-----------------+-----------------+-----------------+ \* Anemophilous (wind-pollinated); Others are entomophilous (insect-pollinated). \*\* In muskmelon most of the varieties are andromonoecious, while some are monoecious. Broadly speaking, the breeding methods for all the cross pollinated vegetable crops are the same since they have similar breeding system. However, the breeding methods differ in some respects in these vegetables, particularly those which have self-incompatibility, dioecious or monoecious sex form and biennial or perennial growth habit. The extent of loss of vigour due to inbreeding, a general characteristic feature of cross-pollinated vegetables, will also necessitate modification of breeding procedures to some extent. Among the temperate vegetables, varieties falling under cole crops are important and are widely grown. All these vegetables are cross-pollinated. Pollination is being carried out mostly by insects notably honey bees. From the breeding point of view, cabbage and allied vegetable crops have various important characteristics in common. i. Most botanical varieties of *Brassica oleracea* are biennial, flower after the winter (over wintering), because a period of low temperature (0°-7°C) is required for flower formation. ii. Cole vegetables are usually cross-pollinated, but in some cauliflower varieties, seed setting is partly brought about by selfing. iii. It is possible to judge the quality before flowering and this increases the effectiveness of selection. For most vegetables seed production, the cycle followed is as grown as usual, selection-vegetative phase, maintenance-over wintering (through out the winter) bolting-flowering-pollination by insects (after the end of winter). The breeding procedures for cole vegetables are not much different from other cross-pollinated vegetables, however, the varying degrees of self-incompatibility plays a great role in breeding programmes. Self-incompatibility -------------------- Which prevent [self-fertilization](http://en.wikipedia.org/wiki/Self-fertilization) and thus encourage [out crossing](http://en.wikipedia.org/wiki/Outcrossing). Self-incompatibility means where both male and female parts are capable of producing normal gametes but fails to set seed. The advantages of self-incompatibility have been utilized in the production of hybrid seed in vegetable crops. Also it is important to know the mechanism of self-incompatibility if the various vegetables are to be maintained through selfing and crossing. Advantages of using self-incompatibility over male sterility ------------------------------------------------------------ i. There is no need for the maintainer lines ii. The seed set takes place on both the parents Disadvantages of using self-incompatibility over male sterility --------------------------------------------------------------- i. The incompatibility mechanisms are complex ii. The incompatibility mechanisms are influenced by environment. **Types of self-incompatibility mechanism** Homomorphic Heteromorphic **Homomorphic** There is no morphological difference in the male and female organs which hinders their compatibility, within the same flower / plant. This system is prevalent in vegetable crops. Heteromorphic ------------- As an example it is found in evening primrose (Primula) where two types of anthers are found (pin and thrum type) such that pin crosses with thrum and thrum crises with pin. It is not important in vegetables. Gametophytic ------------ Under the homomorphic system, gametophytic system is fairly wide spread. It means that the incompatibility reaction is right in the gametophyte itself i.e. the pollen. This system is prevalent in some plants of the family solanceae and leguminoceae. Sporophytic ----------- This is one of most important types of self-incompatibility found in vegetable crops especially crops belonging to the family cruciferae. In this type, the incompatibility reaction is imparted upon the gametophyte, by the sporophyte parent i.e. the gamete irrespective of their own genotype behaves as per the phenotype of the parent on which they have been produced. The incompatibility reaction appears to be a biochemical process under simple genetic control. The incompatibility process can operate at any stage between pollination and fertilization. Male sterility -------------- One of the outstanding achievements in plant (vegetable) breeding over the last four decades has been the utilization of male sterility in the production of hybrid seed. Discovery of male sterile clones in onion by Jone and Emsweller (1936) led to a search of male sterility in other crop species for their possible use in hybrid seed production. So as to capitalize male sterility for hybrid seed production in vegetable crops, two factors are of prime importance, first how male sterility is inherited, second its manifestation. Types of male sterility ----------------------- Basically three systems of inheritance of male sterility has been recognized, (i) cytoplasmic (ii) genic and (iii) cytoplasmic genic. Male sterility is imparted upon the individual through its cytoplasm. Cytosterile plants shall always need a pollinator for their maintenance and also for seed production in the hybrids. The male sterility in these crops is controlled by a single recessive gene which is maintained by a hetrozygous pollinator. In every generation, fifty per cent of the plants have to be rogued out from the female lines as they are male fertile. (E.g) tomato, lettuce, cowpea, lima bean, watermelon and muskmelon. iii\. The cytoplasmic genic male sterility behaves just as cytoplasmic type of sterility and has the same practical bearings like rendering the F~1~ seed male sterile. But an important difference lies in the interaction of cytoplasmic and nuclear genes, for the cytoplasm to cause male sterile in this case it has to be accompanied by recessive male sterile gene(s) in the cytoplasm. Thus, this type of sterility has been made use in production of hybrid seed on large scale in onion, where it is controlled by sterile cytoplasm and a recessive nuclear gene and in garden beet where it is controlled by sterile cytoplasm and two recessive genes. **Annuals: Seed to seed method** **Biennials: i. Insitu method** **ii. Transplanting method (Seed to Head, Seed to bulb)** **Method /systems of hybrid seed production used in vegetable crops** **S.No** **Hybrid seed production mechanism** **Commercially exploited crops** ---------- --------------------------------------------------------------- --------------------------------------------- 1. Hand emasculation and manual pollination Tomato, Brinjal, Sweet pepper, Okra, Chilli 2. Pinching of staminate flowers and hand pollination Bitter gourd, Bottle gourd, pumpkin 3. Removal of staminate flower + emasculation + hand pollination Watermelon and muskmelon 4. Functional male sterility and hand pollination Tomato, Brinjal 5. GMS + bee pollination Chilli 6. CMS + natural pollination Capsicum, onion, cabbage, carrot, radish 7. Self Incompatibility and natural pollination Cauliflower , broccoli 8 Gynocecism and natural pollination Cucumber , bitter gourd 9 PGR and natural pollination Squash's 10 Detasseling + wind pollination Sweet corn, baby corn **Mechanisms for hybrid seed production in vegetable crops:** 1. **Gynoecious sex form:** The hybrids of cucumber are produced mainly by crossing gynoecious lines with monoecious lines. The other systems of producing gynoecious hybrid seed are gynoecious × gynoecious but gynoecious × monoecious hybrids are still widely grown hybrids because this offers advantages like earliness (Jat et al., 2015), high degree of female sex expression (Jat et al., 2016; Jat et al., 2017), with uniform and concentrated fruit formation, which was especially advantageous for mechanical harvest (Robinson 1999, 2000). **Use of growth regulators for maintenance of gynoecious lines in** **cucurbitaceous crops**: Gynoecy is most important sex form which has made phenomenal exploitation of hybrid vigour in cucumber, bittergourd and muskmelon (Munshi et al., 2017). The gynoecious inbreds could self reproduce if a growth regulator is applied to induce male flowers (Robinson, 1999). The gibberellic acid (1500-2000 ppm) is used for induction of male flower in cucumber. (Peterson and Anhder (1960) but different gynoecious lines vary in response to GA application and the number of induced male flowers are not sufficient for hybrid seed production, cause excessive stem elongation or malformed male flowers (Robinson, 2000). Therefore, the application of silver compound such as silver nitrate (250-400 ppm) is done to induce male flowers. These ions inhibit ethylene action and promote male flower induction in gynoecious cucumber lines (Beyer, 1976). However, due to phytotoxic effects of silver nitrate such as burning of plants, now a day's silver thiosulphate (400 ppm) is widely used by seed producers for the maintenance of gynoecious cucumber lines. It induces Advances in Quality Seed Production of Vegetable Crops CAFT 2017-18 29 male flowering of cucumber plants over a longer period and is less phytotoxic compared to silver nitrate. **2. Male sterility system**: Genetic male sterlity systems have been utilized for commercial hybrid production in muskmelon (Punjab Hybrid-1). The female and male are grown in 4:1 ratio. However, to maintain the good plant population in female rows it is suggested that seed parent should be sown with double seed rate. It is also advised that female line seedling should be raised in polythene bags and transplanted at flower appearance in order to avoid the fertile plants in female rows. The pollination is done by honey bees. The male sterile line is maintained in heterozygous form by crossing with maintainer line under adequate isolation distance or under cover. Among the genetic emasculation tools, both genetic male sterility (GMS) and cytoplasmic genetic male sterility (CGMS) have been employed in hybrid seed production of chillies. Using these male sterile lines, hybrid cultivars (Kashi Surkh from IIVR, Varanasi; Arka Meghana, Arka Sweta and Arka Harita from IIHR, Bangalore) were identified for commercial exploitation. **Use of chemicals for sex modification of cucurbits for hybrid seed** **production**: Specific chemicals are known to induce female and male flowers in cucurbits as desired. Ethrel (2-choloro-ethyl-phosphonic acid) 200-300 ppm at two and four true leaf stage and another at flowering is useful for inducing the pistilate flower in bottle gourd, pumpkin and squash for F1 seed production. The row of male parent is grown side by the side of female and natural cross pollination is allowed. The complete suppression of male flowers in squash can be achieve at higher concentration of (400-500 ppm) of ethrel and nearly 56% of total squash seed produced in USA is of F1 hybrid. The other chemicals like GA3, (10-25 ppm) in cucumber, MH-(100 ppm), ethephone (600 ppm) in squash induces female flowers.